1. Field of the Invention
The present invention relates to a metal insulator metal field emission display device and particularly, to an apparatus and method for driving a metal insulator metal device which are capable of removing electric charge charged in the pixel cell inside a panel.
2. Description of the Background Art
Recently, various metal insulator metal (hereinafter, as MIM) display devices which can reduce weight and volume of a Cathode Ray Tube (hereinafter, as CRT) have been developed. The metal insulator metal display device is divided to a Liquid Crystal Display (hereinafter, as LCD), Field Emission Display (hereinafter, as FED), Plasma Display Panel, Electro-Luminescence (hereinafter, as EL) and the like. To improve the displaying quality of the metal insulator metal display device, researches for increasing luminescence, contrast and colorimetric purity are actively in progress.
The FED is divided into a tip type FED which emits electron using the tunnel effect by concentrating a high electric field in the acute emitter, and a MIM FED which emits electron by concentrating a high electric field in a metal having a predetermined area.
FIG. 1 is a cross-sectional view showing a pixel cell of a MIM FED display device in accordance with the conventional art.
As shown in FIG. 1, the pixel cell of the MIM FED includes an upper glass substrate 2 which is laminated on an upper portion of an anode electrode 6, fluorescent material 12 which is deposited in a predetermined portion of the lower portion of the anode electrode 6, and a field emission array 16 which is formed on a lower substrate 4. The field emission array 16 includes a scan electrode 10 which is formed on the lower substrate 4, an insulation layer 14 which is formed on the scan electrode 4, and a data electrode 8 which is formed on the insulation layer 14. Hereinafter, the operation of the MIM FED will be described as follows.
First, the scan electrode 10 supplies a current to the insulation layer 14, the insulation layer 14 insulates between the scan electrode 10 and data electrode 8, and the data electrode 8 is used as a fetching electrode for fetching electrons. Also, the scan electrode 10 receives a scan pulse from the scan driving unit (not shown) and the data electrode 8 receives a data pulse from the data driving unit (not shown).
To display an image on the display device, firstly, a voltage of a positive polarity (plus+) is applied to the anode electrode 6 on the upper substrate 2. At this time, a voltage of a negative polarity (minus−) is received in the scan electrode 10 on the lower substrate 4 and a voltage of the positive polarity (plus+) is applied to the data electrode 8. That is, part of the electrons tunnels the insulation layer 14 and electrons having a high level of energy among the above electrons pass through the insulation layer 14 and data electrode 8 and is emitted to a vacuum space. The emitted electrons are bumped into the red, green and blue fluorescent material 12 and excite the fluorescent material 12. At this time, a visible ray of a color among red, green and blue colors is emitted according to the fluorescent material 12.
FIG. 2 is a wave view showing a driving wave form which is supplied to the MIM FED display device in accordance with the conventional art.
As shown in FIG. 2, a scan pulse SP of a negative polarity (minus−) is sequentially supplied to the scan lines S1˜Sm of the MIM FED display device in accordance with the conventional art and a data pulse DP of a positive polarity (plus+) which is synchronized with the scan pulse of the negative polarity (minus−) is sequentially supplied to the data lines D. In the pixel cell to which a scan pulse SP and data pulse DP are supplied, electrons are emitted by voltage difference of the scan pulse SP and data pulse DP. This will be described with reference to FIG. 3.
FIG. 3 is a circuit view equivalently showing the driving unit and discharging cell, for applying a driving wave form to the scan line which is shown in FIG. 2.
As shown in FIG. 3, the scan driving unit includes a scan pulse supply unit 20 for generating a scan pulse, a scan drive Integrated Circuit (hereinafter, as IC) 22 for supplying the scan pulse SP which is supplied from the scan pulse supply unit 20 to a scan line S1 among scan lines S1˜Sm, and a resistor R which is installed between the IC 22 and ground voltage source (hereinafter, as GND).
The scan pulse supply unit 20 includes first and second switches SW1 and SW2 which are installed in parallel between the GND and scan drive IC 22, a third switch SW3 which is installed between the scan pulse voltage source Vs and scan drive IC 22, and a fourth switch SW4 which is installed between a reset pulse voltage source Vr and scan drive IC 22.
The first to fourth switches SW1˜SW4 turns on/off in respond to a control signal which is supplied from the timing control unit (not shown). That is, the first switch SW1 and third switch SW3 respond to the control signal which is supplied from the timing control unit in turn and supplies a scan pulse SP to the corresponding scan lines S1˜Sm. The second switch SW2 and fourth switch SW4 supplies a reset pulse RP to all scan lines S1˜Sm by responding to the control signal which is supplied from the timing control unit.
The first switch SW1 raises the scan pulse SP of a negative polarity (minus−) into the GND and the third switch SW3 supplies a scan pulse SP of a negative polarity (minus−). Also, the second switch SW2 operates oppositely to the fourth switch SW4 and lowers the scan pulse SP to a negative polarity (minus−). The fourth switch SW4 supplies a reset pulse RP to all scan lines S1˜Sm.
On the other hand, the resistor R is a resistance for reducing a peak current when a voltage is instantaneously applied to the scan drive IC 22 and is a resistance protection device.
Hereinafter, the operation of the driving unit will be described with reference to FIG. 2.
First, the scan pulse SP of a negative polarity (minus−) is supplied from the scan pulse voltage source Vs to the first scan line S1 through an internal diode of the scan drive IC 22, when the third switch SW3 and second switch SW2 are turned on under the condition that the first and fourth switches SW1 and SW4 are turned off. The data pulse DP is supplied to the data electrode D in synchronization with the scan pulse SP of a negative polarity (minus−).
When the first switch SW1 is turned on at the same time as the third switch SW3 is turned off, the first scan line S1 receives a zero potential (GND) by the first switch 58.
Then, second switch SW2 is turned off when the scan pulse SP is supplied to all scan lines S1˜Sm, and on the other hand, the fourth switch SW4 is turned on, thus to supply the reset pulse RP of a positive polarity (plus+) from the reset pulse voltage source Vr.
By repeating such process, an image is displayed by driving a pixel cell by sequentially applying the scan pulse SP and data pulse DP to the mth scan line Sm. After displaying the image, the reset pulse of a positive polarity (plus+) is applied to the first to mth scan lines S1˜Sm. That is, when the reset pulse RP is applied to the first to mth scan lines S1˜Sm, electric charge which is charged in the pixel cell is removed.
The reset pulse RP is supplied from the reset pulse voltage source Vr to all scan electrodes S, when the fourth switch SW4 of the scan pulse supply unit is turned on. At this time, the reset pulse is flowed to the scan electrode S through the internal diode of the scan drive IC 22. An output impedance of the scan drive IC 22 is changed by the resistor R which is connected between the GND and output terminal of the scan drive IC 22. Also, as the number of the scan line increases, (namely, as resolution increases), the whole output impedance is also changed and the voltage of the reset pulse RP is decreased as the voltage for supplying the reset pulse by the output of the switching device and resistance of the output side. This will be described with reference to FIG. 4.
FIG. 4 is a wave view showing the conventional reset pulse that the amplitude change was occurred.
As shown in FIG. 4, the amplitude A of the reset pulse RP which is supplied to all scan electrodes S by the change of the output impedance of the scan drive IC 22 (the whole output impedance is changed according to increase/decrease of number of the scan lines) is decreased lower than the amplitude which is supplied from the reset pulse voltage source Vr. That is, since the amplitude A of the reset pulse RP is changed as the output impedance of the scan pulse supply unit 20 changes, the electric charge which is charged in the pixel cell could not be completely removed. Also, as the charge which is charged in the pixel cell could not be completely removed, current leakage which flows from the pixel cell to the GND through the resistor R was occurred, thus to decrease life span of the MIM FED.
As described above, in the MIM FED in accordance with the conventional art, the amplitude A of the reset pulse RP is changed as the output impedance of the scan pulse supply unit 20 changes and accordingly, the electric charge which is charged in the pixel cell could not be completely removed.
Also, in the MIM FED in accordance with the conventional art, the electric charge which is charged in the pixel cell could not be completely removed and accordingly, current leakage which flows from the pixel cell to the GND through the resistor R is occurred, thus to decrease the life span.